Conventionally, metal oxide semiconductor (MOS) transistors are fabricated on predoped semiconductor substrates. A typical MOS transistor has a source, a gate, and a drain. The gate is separated from the predoped substrate by an insulative layer. Electric current flows in a channel between source and drain under control of voltages applied to the gate. In particular, electric current flow in the channel can be modulated by applying time-varying signal voltages to the gate electrode. An electric potential applied to the gate electrode either enhances or depletes the channel region of its ability to transmit current, and thereby controls the flow of current between the source and drain electrodes.
Junction field effect transistors (JFETs), on the other hand, have a PN junction at the gate which can be reverse biased by the application of a voltage to the gate. The gate PN junction accordingly controls the channel current by varying the extent of a depletion region which in turn narrows or widens the channel.
MOS transistors are widely used for analog applications. However, they have undesirable noise characteristics and suffer slow operating speeds. Semiconductor circuits and methods promoting improved noise characteristics and faster current modulation are desirable.